Molecular chaperones ensure protein quality during protein synthesis, delivery, damage repair, and degradation. The ubiquitous and highly conserved molecular chaperone 70-kDa heat-shock proteins (Hsp70s) play essential roles in maintaining protein homeostasis by cycling through high and low affinity binding of unfolded protein clients to facilitate folding. Hsp110s are divergent relatives of Hsp70s that are highly efficient in preventing protein aggregation but lack the hallmark folding activity seen in Hsp70s. Hsp110s serve as Hsp70 nucleotide exchange factors (NEF) and facilitate the Hsp70 folding cycle by inducing release of protein substrate from Hsp70, thus recycling the chaperone for a sequential round of folding and allowing successfully folded substrates to exit the folding cycle. In the model organism Saccharomyces cerevisiae, Hsp110 is represented by the proteins Sse1 and Sse2, which possess a substrate binding domain (SBD) like the Hsp70s, making them unique among other functionally similar, but structurally distinct, NEFs. Studies of Hsp110 and Sse1 have demonstrated that the chaperone/NEF family can bind polypeptides and prevent proteins from aggregating in vitro and this ability is conferred by the SBD. However, attempts to study Hsp110 protein binding in vivo have not been successful. To date, the impact of peptide binding by Hsp110 is unknown. Here, I propose to (1) elucidate and define substrate binding by yeast Hsp110 and (2) define the contributions of this activity toward protein and cellular homeostasis. As a major partner of Hsp70, determining Hsp110 activities in the cell is a prerequisite to full understanding of chaperone-mediated protein homeostasis. By studying chaperone functions and activities in yeast, we can understand human cellular protein quality control systems which can then be pharmacologically targeted to combat protein conformational disorders, including Alzheimer's, Huntington's and Parkinson's diseases.